CA-146138: don't refresh slaves for local SRs

Don't try to synchronise logical volumes on other slaves for a SR that
is local to the host, it doesn't make any sense and can cause all sorts
of problems.

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>
Reviewed-by: Mate Lakat <mate.lakat@citrix.com>
CA-146138: improve error message when srcmd.params is malformed

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>
Reviewed-by: Mate Lakat <mate.lakat@citrix.com>
CA-146138: unit test for LV refresh on other hosts

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>
Reviewed-by: Mate Lakat <mate.lakat@citrix.com>
CA-146138: various improvements over unit test

Signed-off-by: Mate Lakat <mate.lakat@citrix.com>
Reviewed-by: Thanos Makatos <thanos.makatos@citrix.com>
Merge branch 'CA-146138' into xs64bit

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>

GitHub: closes #221 on xapi-project/sm